Common blanking dies are known, for example for producing magnetic laminations and/or magnetic lamination packs for electric motors and generators. These dies usually present a lower part and an upper part. These two parts are mutually aligned by guide columns. The die upper and lower parts present corresponding substantially flat portions known respectively as the flat lower portion or die plate and the flat upper portion or punch guide plate or punch stripping plate. With the die open, sheet metal in the form of a strip is fed to the die, to rest on the die plate. The die upper part presents a plurality of punches which project from the punch guide plate during blanking, when the die is closed by the action of the press. The punches then blank the laminations. For blanking purposes, recesses are provided in the die plate in positions corresponding with the punches, to receive said punches in order to implement the blanking operation. On closing the die, the punches press on the sheet metal in positions corresponding with the portion under which the relative recesses lie. Blanking is then achieved by cutting forces which the punches generate on the sheet metal at the recesses.
A part of the die upper portion located above the punches is known as the closure plate. The closure plate can be opened/disassembled (completely or partly) to replace the punches.
This solution presents however various drawbacks linked to punch replacement. In this respect, the punches need to be replaced following breakage/wear or because of changing conditions which produce results outside the required tolerance ranges. Punches are usually replaced after opening and totally or partially dismantling the closure plate. However, as the punch replacement operation involves disassembly of the die, there is consequent stoppage of the blanking operations and interruption of production. This replacement operation can last many hours, and only afterwards can die productivity be resumed.